Drinking a half-liter of beetroot juice before a time trial helped male bicycle racers ride an incredible 2.8 percent faster over both 4- and 16-kilometer courses (Medicine & Science in Sports & Exercise, June 2011). This is an extremely well-performed study because all of the bicycle racers in the study rode faster after drinking a half- liter of normal beetroot juice (6.2 mmol nitrate) than they did after taking the same volume of beetroot juice that had had the nitrates removed (0.0047 mmol nitrate). Furthermore, the authors measured blood levels of nitrates and showed that the nitrate-rich beet juice raised blood levels of nitrates from 241 to 575 nm and reduced the oxygen cost of the exercising muscles. The dose of nitrate used in the study (6.2 mmol) is 4 to 12 times greater than what the average person takes in each day. None of the subjects consumed dietary supplements.

Any food source of nitrates, not just beetroot juice: Beetroot juice is high in nitrates which have been shown in many studies to reduce the amount of oxygen needed to fuel muscles during exercise and to improve an athlete’s ability to tolerate high-intensity exercise. How fast you can race on a bike is limited by the time it takes to bring oxygen into exercising muscles to turn food into fuel for contracting muscles. Since nitrates bring oxygen faster into muscles, eating any food that is high in nitrates can help you ride faster.

How nitrates make you faster: Inorganic nitrate is converted to active nitrite and, subsequently, to nitric oxide (Nat Med. 2003;9:1498-505). The most efficient form of energy for exercising muscles comes from your mitochondria in muscles which require less oxygen after a person takes nitrates (Free Radic Biol Med. 2010;49:S109).

How much nitrate before racing? In this study, the racers were given liquids because liquids pass through their stomachs and into their bloodstreams much faster than solid foods do. You can get large amounts of nitrates from celery, cress, lettuce, radishes, beets, spinach, Chinese cabbage, endive, kohlrabi, leeks, parsley and many other vegetables (Am J Clin Nutr. 2009 Jul;90(1):1-10). Almost all of the nitrates in vegetables are absorbed into the bloodstream.

Can you take in too much nitrate? Nitrates are safe and healthful when eaten in vegetables and fruits. However, nitrates can be converted to nitrites which can combine with amino acids in foods to form nitrosamines which are potent cancer-causing agents. Nitrates (with an A) in plants are healthful. Too much nitrites (with an I) can be harmful.

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Avoiding nitrites: Bacteria convert the healthful nitrates to the harmful nitrites in vegetables. Fresh vegetables are usually resistant to bacterial infections. However, once a vegetable is cooked, bacteria reduce nitrates to nitrites. Therefore, cook only the amount of a vegetable that you plan to eat right away. Leftovers should be stored for no more than a day or two in the refrigerator. Freezing inactivates bacteria, so commercially frozen cooked vegetables usually have low levels of nitrites. Pureed foods are much higher in nitrites. Boiling vegetables reduces nitrate content (Toxicol Lett. 2008(Oct 1);181(3):177-81).

Should you take nitrate pills? Definitely not! Excessive nitrates in grass and grains have killed ruminant animals. Bacteria in the stomachs of ruminant animals rapidly reduce nitrates (with an A) to nitrites (with an I). Normally, the nitrites are converted to ammonia to be used by bacteria as a source of nitrogen, but nitrites can convert hemoglobin in blood to methemoglobin, which cannot carry oxygen and the animal can smother to death.

In humans, excessive nitrites can accumulate also and prevent oxygen from attaching to red blood cells. This is called methemoglobinemia which can prevent you from even being able to move, and has killed some infants and adults. This condition can be caused by drinking very large amounts of stale juice from cooked spinach or other vegetables high in nitrates. On the other hand, you should not worry about nitrates in fresh vegetables harming you.

Should you eat vegetables containing nitrates all the time? So far, nobody has proven that a high vegetable diet will make you a better athlete. It was relatively easy to set up a study in which a single dose of nitrates is given before a time trial. However, it takes far more planning and work to set up studies in which athletes are on long-term, high-vegetable diets and compare them to other athletes on low-vegetable diets. We have to await further research to prove that a high-plant diet will make you a better athlete. I think it will.

Nitrates help to prevent heart attacks: I recommend that you eat a high-vegetable diet anyway because it can prolong your life and help to prevent certain cancers, heart attacks and many other diseases. The Mediterranean Diet and the DASH Diet have both been shown to lower cholesterol and blood pressure, and help to prevent heart attacks. These diets are high in fruits and vegetables that are rich sources of nitrates. Many studies show that nitrates in vegetables lower high blood pressure. (Hypertension. 2010;56:274-81). They do this by widening blood vessels to increase oxygen availability to muscles. Nitrates also help prevent heart attacks during intense exercise (Cardiovasc Res. 2011(Feb 15);89(3):499-506).

Dear Dr. Mirkin: Should I take antioxidant pills as part of my training program?

No; the current issue of Journal of the American College of Sports Medicine shows that antioxidant pills prevent the major mitochondrial benefits of athletic endurance training (Medicine & Science in Sports & Exercise, June 1, 2011). Rats that trained on a treadmill increased the enzymes that are necessary to increase the number and size of mitochondria. Rats who trained on a treadmill and were given two powerful antioxidants, vitamin E and alpha lipoic acid, did not increase the enzymes that are necessary to increase the number and size of mitochondria.

How humans get their energy for exercise: Humans convert food to energy most effectively in the mitochondria, hundreds of small chambers inside muscle fibers. They need oxygen to do this. The limiting factor to how fast and long you can move is the time it takes to move oxygen into muscle fibers. Athletic training makes you faster and gives you greater endurance by enlarging and increasing the number of mitochondria in muscles.

Antioxidant pills can harm: People who take 1000 mg/day of vitamin C and 400 IU/day of vitamin E do not gain the benefits of increased insulin sensitivity when they exercise (Proceedings of the National Academy of Sciences, May 12, 2009).

• When blood sugar levels rise too high, sugar sticks on the surface of cell membranes and can never get off. The attached sugar is converted in a series of chemical reactions to sorbitol that destroys cells.

• Contracting muscles help to prevent this damage by removing sugar so fast from the bloodstream that blood sugar levels do not rise too high.

• Food is converted to energy to power your muscles by a series of chemical reactions that shuffle electrons from molecule to molecule.

• This occurs primarily in the mitochondria, small energy-producing chambers in cells, that number anywhere from a few to thousands in each cell.

• As electrons are shuffled to produce energy, extra electrons can accumulate. They can either end up on hydrogen atoms to form water and become harmless, or they can end up on oxygen atoms to form free radicals that can damage cells. This can cause cancers, heart attacks and other life-shortening conditions.

• Exercise speeds up the reactions that turn food into energy, so exercise increases the production of free radicals.

• The body responds to this increased production of free radicals during exercise by producing tremendous numbers of antioxidants that sop up the free radicals and render them harmless.

• Exercise prolongs life and prevents heart attacks and cancers by causing the body to dispose of free radicals by the increased production of antioxidants.

Let the buyer beware: If you exercise and take antioxidant vitamins C and E, you prevent your own body from making large amounts of antioxidants during exercise, so more free radicals (oxidants) accumulate in your body and more cells are damaged.

Many studies show that:

• Taking large doses of beta carotene (pro-vitamin A) increases risk for heart attacks in men and increase risk for lung cancer in smokers.

• Taking large doses of vitamin C does not prevent colon cancer, and does not prolong life in people with cancer.

• Taking large doses of vitamin E or selenium does not prevent lung cancer, heart disease or stroke.

My recommendations: Exercise every day, and get the antioxidant vitamins and other nutrients your body needs from foods, not from pills. Eat a wide variety of foods including large amounts of fruits, vegetables, whole grains, beans, nuts and other seeds. If you want to take Recommended Dietary Allowances of vitamins in pills, go ahead; there is little evidence that you will harm yourself. However, when you take large doses of any vitamin, you don’t have the foggiest idea whether you are harming or helping yourself. I do not recommend large doses of vitamins to anyone.

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Dear Dr. Mirkin: Is it harmful to drink five beers on Saturday if I have no alcohol the rest of the week?

Yes! That is called binge drinking. Taking more than 2 drinks a day on a regular basis will shorten your life and increase risk for certain cancers, heart attacks and strokes. A drink is five ounces of wine, 12 ounces of beer and 2/3rds of shot glass. Taking more than two drinks a day, just once a week, can impair your memory. Binge drinking students perform worse on memory tests, both on immediate and delayed recall (Alcoholism: Clinical and Experimental Research, published online May 16, 2011).

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., and his wife, nutritionist Diana Mirkin bring you news and tips for your healthful lifestyle. A practicing physician for 50 years more

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